Globio

Glossopedia

There's More to Light Than Meets the Eye

Light is a form of energy. We see it in many
different forms all around us. It’s the sunlight that pours through your
bedroom window and wakes you up. It’s the glow of your computer screen
and the flash of lightning during a thunderstorm. It’s the crackling
flames in a fireplace. All are forms of light.

Fire is a source of both light and heat. Fire gives off different amounts
of light and appears to us as different colors. Take a closer look at a candle
flame, camp fire, or fire in a fireplace and see what colors you notice.

These are all forms of visible light – the light we can see. But visible
light is only a narrow sliver of the universe’s light energy. Most light
energy is invisible.
Scientists refer to all forms of light energy — the visible and the invisible — as electromagnetic
radiation.

Incandescent Light Is Hot Stuff

The Sun is a giant ball of burning gas that gives off a lot of light. This
light is what makes life on Earth possible. Plants need the Sun’s light
to grow and make oxygen. Without the Sun, Earth would not be a very green
planet.

Visible light can be produced in many ways.
Most commonly light is produced when something becomes very hot, or incandescent.
The Sun is
our biggest and most important source of incandescent light. With a surface
temperature of about 5500° C,
the Sun produces vast amounts of visible and invisible light.

An electric light bulb gives off light when electricity heats up a filament to
about 2200° C,
causing it to glow. If you’ve accidentally touched a glowing light bulb,
then you know it’s a source of hot, incandescent light. Ouch!

A light bulb is a source of incandescent light. This kind of light is produced
with heat which is why most light bulbs have protective covers or shades
around them. This is also why we have to be careful when decorating with
strands of light bulbs.

Luminescent Light: It Glows

A firefly might look like it is carrying a tiny light bulb but it is actually
making its own light. Some animals make light by changing chemicals in their
bodies. This makes them glow, just like a bulb or tiny flame.

Light made without heat is luminescent light.
Running an electric current through
a gas causes
the gas to temporarily absorb energy and then give off light without also producing
heat. This is how fluorescent and neon lights work.

Some plants and animals give
off light by changing chemical energy in their bodies into light energy. This
kind of light is called bioluminescence.
Fireflies that flicker on and off on summer nights are bioluminescent.

What Do Waves Have to Do with Light?

Light can be seen in many colors but what we normally think of as light,
is usually white light. White light is all the colors mixed together and
is what a lamp or flashlight might give off.

Light energy behaves like a wave. Like all
waves, light waves have wavelengths and frequencies.
Light from the Sun or a table lamp is white light, which is actually a blend
of light of different colors known as the visible
spectrum.

How Can Light Make Electricity?

People have created technology that uses large panels, called solar panels,
that can collect and convert energy from sunlight into energy that can be
used to power appliances or heat a home.

But wait! Light can also behave like a stream
of particles.
These particles are tiny units of light energy called photons.
When photons from a light beam strike certain materials, such as silicon,
they can make electricity. It’s called the photoelectric
effect. The photoelectric effect is what makes solar-powered calculators
work and what makes large solar panels heat a home.

Measuring Light

Stars are very bright, they have what scientists call a high luminous intensity,
but because they are so far away, they often look dim or twinkley to us.
A star that looks very bright must be putting off a lot of light!

The amount of light a source produces is
its luminous
intensity. Scientists measure luminous intensity in units called candelas.
Luminous intensity is not quite the same thing as brightness. Light from sources
that are far away provides less illumination, or surface light, than light
from a nearby source of the same luminous intensity. Distant stars, for example,
pump out tremendous numbers of candelas. But they are so far away they may
not provide any illumination on Earth.

Reflection: The Bouncer

Light rays travel outward in all directions
along a straight path – until they hit something. Then they can bounce,
bend, be absorbed, or be polarized.
Reflection occurs when light bounces off a surface and back to our eyes. This
is how we see objects. Some objects reflect more light rays than others. When
you look in a mirror, the mirror reflects almost all the light that hits it.
The light reflects back at the same angle and you see a clear image of yourself.

Rainbows are just light tricks. All the tiny droplets of rain refract the
sunlight peaking through the clouds. This creates a rainbow.

Refraction: The Bends

When light travels from air to a denser form of transparent matter such as
glass or water, it slows down and bends. This is refraction.
If you’ve ever noticed that a straw in a glass of water looks “broken,” then
you’ve seen refraction in action. Raindrops refract sunlight and disperse it
to form a rainbow.

Absorption: The World in Color

The amount of light reflected and absorbed by objects helps explain why we
see different colors. Most objects absorb some wavelengths of light and reflect
others. For example, a lime looks green. This is because the lime reflects
light in the green wavelength but absorbs light in the other visible wavelengths.

Objects look a certain color to us because of light. This lime looks green
because it reflects only green light. A red car looks red because it absorbs
the light of all the spectrums except red.

How about objects that look black or white? Light hitting an object such as
a glass of milk reflects all the visible color wavelengths.
When the colors of the visible spectrum are blended, they look white. But when
an object looks black, it’s because all the colors are being absorbed
and none are reflected.

Polarization: Sun Block

White light is made of light waves that are vibrating in different directions,
at right angles to the path of the light ray. Passing light through a filter
called a polarizing filter lets only waves that are vibrating in one direction
get through. The light that gets through the filter is polarized, because all
the waves are vibrating in one direction. There are a number of practical uses
for polarization. Polarizing sunglasses, for example, block light waves to
reduce glare.

Bright sunlight isn’t very good for your eyes and can make it hard
to see when it is very bright. Sunglasses can help block some of the light
and if they are polarized can also reduce glare, making it much more fun
to play in the sun.

Early Reflections on Light

Humans have always been curious about light.
The ancient Greeks thought that light traveled out from our eyes to let us
see objects. In about A.D. 1000, an Arab thinker named Alhazen became the first
to recognize that we see objects because light reflects off them.

More Enlightening Discoveries

The scientist Isaac Newton made important discoveries about light that helped
future scientists in their studies.

Several important breakthroughs came in the 1600s. English scientist Isaac
Newton (1642–1727) experimented with prisms and discovered that white
light is a blend of all the colors: red, orange, yellow, green, blue, and violet.
Newton also believed that light was made up of particles. The Dutch scientist
Christiaan Huygens (1629–1695) was the first to suggest that light behaves
like a wave.

Waves or Particles: The Great Debate

Scientists could not agree on whether light behaved like particles or waves.
But in the 1800s, Scottish scientist James Clerk Maxwell (1831–1879)
developed the theory of electromagnetism. His theory identified
light as an electromagnetic wave, that is, a wave produced by electric and
magnetic fields. Finally. That was settled. Light was a wave.

Or was it? In the early 1900s, the particle theory surfaced again. German
scientists Max Planck (1858–1947) and Albert Einstein (1879–1955)
did experiments that suggested that light was given off in tiny packets, or
quanta. This led to the development of quantum
theory; a revolutionary concept that helped explain how light could behave
both like a wave and a stream of particles.

Two Who Turned on the Lights

In the 1870s, American inventor Thomas Edison and British inventor Joseph
Swan found that electricity could be used to heat up a filament so that it
gave off heat and light energy. Placing the filament inside an empty glass
ball allowed it to burn brightly without catching fire. The light bulb was
born. By the end of the 1800s, electric lighting was becoming common in homes,
businesses, and factories, changing life forever. Never again would daily activities
have to end when the sun went down.

Lenses

Light rays that are bent by a lens are what make it possible to see this
tiny chicken embryo. This is the same technology used in telescopes to see
planets and stars in our solar system.

Increased knowledge about how light works
did more than light up our homes. For instance, the understanding of refraction
brought about the invention of the lens.
Lenses bend light rays so that people can clearly see things that are very
small or very distant. Eyeglass lenses correct people’s vision by bringing
fuzzy images into sharp focus. Lenses in microscopes help
scientists see tiny life-forms. Telescope lenses help scientists get a better
look at faraway stars and planets.

Lasers can be used for lots of things. They can be used in special surgery,
to cut metal, and for fun things like this laser show. Without lasers, you
wouldn’t be able to listen to your favorite CD!

Lasers

Einstein’s theories about light helped bring about the invention of
lasers. A laser produces a narrow, high-energy beam of light that is all the
same wavelength. Laser light has an incredible range of uses. The concentrated
energy in laser beams can be used to slice effortlessly through steel. It also
can be aimed very precisely to perform delicate surgery on eyes. Laser beams
are also used to etch information into CDs and DVDs. Lasers also help decode
the information on CDs and DVDs.

Fiber Optics

Another milestone in light technology was the discovery that print, voices,
music, and images could be converted into pulses of laser light and carried
great distances through fiber
optic cables. Most long-distance phone calls on land lines travel over
fiber optic networks. So do your favorite TV shows. Chances are a fiber optic
network is connecting you to the Internet so you can read this article!